This invention concerns inking roller trains for printing presses. In the art of printing presses it is known to provide a train of serially engaged, ink transporting rollers, known collectively as an inking train, which operates to transfer printing ink from an ink fountain to a printing plate cylinder for the purpose of printing an image on a selected medium such as paper by contacting the printing plate cylinder with the medium to be printed.
For purposes of maintaining high print quality and uniformity, it is considered to be of paramount importance that the ink transferred from the ink fountain be applied to the printing plate cylinder with the greatest possible uniformity. Conventional inking trains have included a variety of ink fountain rollers, ductor rollers, vibrating cylinders, and various arrangements of other rollers, all intended to transfer ink uniformly from an ink fountain to a printing plate cylinder.
With the advent of increasing printing press operating speeds it has become increasingly difficult to control and maintain the ink transfer uniformity required for high print quality. For example, many printing presses utilize ductor rollers with alternately contact a pair of rollers such as an ink fountain roller and a subsequent roller, for example, a vibrating cylinder, to transfer ink therebetween. At higher operating speeds, kinetic and kinematic limitations begin to adversely influence the ability of such a ductor roll to transfer ink with adequate uniformity. These and other limitations related to press operating speed thus may have an adverse impact on print quality at higher operating speeds.
Proposed solutions to such problems, relating specifically to the action of ductor rollers, have included the suggestion that the ducting cycle time of the ductor roller be increased to provide fewer ducting cycles thereof in a given press operating cycle. For example, the ductor roller may be cycled to transfer ink from one roller to another only for every second print. This approach may not provide the desired uniformity in many instances as it requires that two impressions be created from a single inking. Thus, the second impression will exhibit a different degree of contrast and line definition than the first.
According to another proposed solution, two ductor rollers operating in alternating or counter-cycle fashion alternately lift ink from a common ink fountain roll which receives the ink directly or indirectly from an ink fountain. This proposed solution also may adversely affect print uniformity as one of such alternately cycling ductor rollers will consistently carry less ink than the other because both are lifting ink from the surface of a common roller. Accordingly, in this instance also the prints or impressions may not be of consistent uniformity or quality.